1. Field of the Invention
The present invention relates to hermetically sealed electric motor compressors for use in household refrigerators, e.g., and more particularly to hermetically sealed electric motor compressors having an improved valve assembly opening and closing a discharge port of a compressor unit and an improved muffler mounted to the discharge port of the compressor unit.
2. Background Art
FIG. 1 is a block diagram illustrative of the arrangement of the components of the of such compressor 1000. The hermetically sealed electric motor compressor 1000 comprises an electric power supply unit 100 receiving electric power from the outside of the compressor 1000, an electric motor 200 receiving electric power from the electric power supply unit 100, a reciprocating compressor unit 300 driven by the electric motor 200, a suction port unit 600 and a discharge port unit 700 which communicate with the interior of the reciprocating compressor unit 300 through a valve assembly 500 mounted to the reciprocating compressor unit 300. The suction port unit 600 has a suction passageway 601. The discharge port unit 700 has a discharge passageway 701. The reciprocating compressor unit 300 sucks refrigerant, e.g., freon through the suction port unit 600 and the valve assembly 500, and compresses and discharges said refrigerant through the valve assembly 500 and the discharge port unit 700. The compressor 1000 further comprises a hermetically sealed casing 900 and a resilient support 800 supporting the electric motor 200, the reciprocating compressor unit 300, the valve assembly 500, the suction port unit 600 and the discharge port unit 700 on the interior surface of the casing 900. The compressor 1000 further comprises a self-lubricating system 400 comprising an oil reservoir. The oil reservoir is mounted on the bottom of the casing 900 and holds lubricating oil 401. The self-lubricating system 400 circulates lubricating oil 401 through mechanically moving parts of the motor 200 and the reciprocating compressor unit 300.
Detailed descriptions of the structures and the operations of the parts described above of the compressor 1000 (referred to as a first prior art hereinafter) are disclosed in U.S. Pat. No. 4,573,880 corresponding to an aggregation of Japanese examined patent application publication SHO. 62-30311, Japanese examined patent application publication HEI. 4-48944 and Japanese examined patent application publication HEI. 4-48945. The disclosure of U.S. Pat. No. 4,573,880 is incorporated herein by the reference thereto.
Since the frequency of reciprocation of the piston of the reciprocating compressor unit 300 is as high-speed as 3,000 times/min, a muffler mounted to the discharge port unit 700 and the structure of the valve assembly 500 have required various improvements.
The first prior art discloses a structure in which a discharge port unit 700 having a muffler comprising, e.g., a series of resonance chambers having different sizes increases an effect of noise reduction.
On the other hand, Japanese examined utility model application publication HEI. 2-25986 discloses the structure of a second prior art in which a valve assembly comprises a reed valve opening and closing a discharge port, and a restraining thick plate mounted behind the reed valve and having sufficient angle of opening so as to restrain the degree of opening of the reed valve and accelerate a return speed of the reed valve to increase the compression efficiency of the reciprocating compressor unit. U.S. Pat. No. 4,723,896 discloses a structure of a third prior art in which a valve assembly comprises a reed valve opening and closing a discharge port, and a restraining plate assembly of leaf springs superposed and disposed in a recess defined in a valve seat behind the reed valve and the restraining plate assembly covers an approximately half of the operating portion of the reed valve covering the discharge port so that the reed valve is twisted to open the discharge port and direct discharged fluid along the axis of the discharge port and so that the torsion from the twisted reed valve accelerates the closing speed of the reed valve.
Since in the valve assemblies of the second and third prior arts simple bending stress and torsional stress in the reed valve assembly of the reed valve and the valve backer return the reed valve to the closed position, the closing speed and the closing force of the reed valve are insufficient so that the reed valve cannot sufficiently follow the discharge pressure of refrigerant and a counterpressure alternating at a high speed to sufficiently reduce the volume of refrigerant returned to the discharge hole. Thus a compressor having the valve assembly of the second or third prior art cannot achieve a sufficient performance of compression.
In addition, since the discharge port having the muffler of the first prior art produces a high pressure at the inlets of the resonance chambers to produce a high discharge resistance when the fluid is discharged from a shut-off valve of the valve assembly, this discharge resistance degrades the compression efficiency and causes the muffler to insufficiently deaden noise.